Theory suggests that relations between authorities affect implementation. This article studies the link between central and local government agencies in the Swedish labour market sector. The analysis is based on new quantitative data. The results indicate that central and local government agencies have very different priorities, but they nonetheless cooperate to a considerable extent. However, cooperation and ‘good’ implementation only coincide under certain conditions. If the collaborative endeavours are explicitly designed to lead to implementation of a specific and demanding task, cooperation is positively related to implementation performance. Agencies that collaborate to a considerable extent at a general level do not, however, perform better than others. Thus, I argue that theories should be developed and tested to indicate when cooperation between public authorities will promote implementation, instead of assuming that cooperation, in general, is a ‘good thing’.